WebClient Class

Inheritance Hierarchy

System.Object
  System.Net.WebClient

Syntax

'Declaration
Public Class WebClient

public class WebClient

Constructors

	Name	Description
	WebClient	Initializes a new instance of the WebClient class.

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Properties

	Name	Description
	AllowReadStreamBuffering	Gets or sets a value that indicates whether to buffer the data read from the Internet resource for a WebClient instance.
	AllowWriteStreamBuffering	Gets or sets a value that indicates whether to buffer the data written to the Internet resource for a WebClient instance.
	BaseAddress	Gets or sets the base URI for requests made by a WebClient.
	Credentials	Gets or sets the network credentials that are sent to the host and used to authenticate the request.
	Encoding	Gets and sets the Encoding used to upload and download strings.
	Headers	Gets or sets a collection of header name/value pairs associated with the request.
	IsBusy	Gets a value that indicates whether a Web request is in progress.
	ResponseHeaders	Gets a collection of header name/value pairs associated with the response.
	UseDefaultCredentials	Gets or sets a Boolean value that controls whether default credentials are sent with requests.

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Methods

	Name	Description
	CancelAsync	Cancels a pending asynchronous operation.
	DownloadStringAsync(Uri)	Downloads the resource at the specified Uri as a string.
	DownloadStringAsync(Uri, Object)	Downloads the resource at the specified Uri as a string.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetWebRequest	Returns a WebRequest object for the specified resource.
	GetWebResponse	Returns the WebResponse for the specified WebRequest using the specified IAsyncResult.
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	OnDownloadProgressChanged	Raises the DownloadProgressChanged event.
	OnDownloadStringCompleted	Raises the DownloadStringCompleted event.
	OnOpenReadCompleted	Raises the OpenReadCompleted event.
	OnOpenWriteCompleted	Raises the OpenWriteCompleted event.
	OnUploadProgressChanged	Raises the UploadProgressChanged event.
	OnUploadStringCompleted	Raises the UploadStringCompleted event.
	OnWriteStreamClosed	Raises the WriteStreamClosed event.
	OpenReadAsync(Uri)	Opens a readable stream to the specified resource.
	OpenReadAsync(Uri, Object)	Opens a readable stream to the specified resource.
	OpenWriteAsync(Uri)	Opens a stream for writing data to the specified resource. This method does not block the calling thread.
	OpenWriteAsync(Uri, String)	Opens a stream for writing data to the specified resource. This method does not block the calling thread.
	OpenWriteAsync(Uri, String, Object)	Opens a stream for writing data to the specified resource, using the specified method. This method does not block the calling thread.
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	UploadStringAsync(Uri, String)	Uploads the specified string to the specified resource. This method does not block the calling thread.
	UploadStringAsync(Uri, String, String)	Uploads the specified string to the specified resource. This method does not block the calling thread.
	UploadStringAsync(Uri, String, String, Object)	Uploads the specified string to the specified resource. This method does not block the calling thread.

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Events

	Name	Description
	DownloadProgressChanged	Occurs when an asynchronous download operation successfully transfers some or all of the data.
	DownloadStringCompleted	Occurs when an asynchronous resource-download operation is completed.
	OpenReadCompleted	Occurs when an asynchronous resource-read operation is completed.
	OpenWriteCompleted	Occurs when an asynchronous operation to open a stream to write data to a resource completes.
	UploadProgressChanged	Occurs when an asynchronous upload operation successfully transfers some or all of the data.
	UploadStringCompleted	Occurs when an asynchronous string-upload operation completes.
	WriteStreamClosed	Occurs when an asynchronous write stream operation completes.

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Remarks

The WebClient class uses the WebRequest class to provide access to resources.

You must use the WebClient class from a Silverlight control that is hosted in a Web page.

The following table describes WebClient methods for uploading data to a resource.

The following table describes WebClient methods for downloading data from a resource.

You can use the CancelAsync method to cancel asynchronous operations that have not completed.

A WebClient instance does not send optional HTTP headers by default. If your request requires an optional header, you must add the header to the Headers collection.

Some headers are considered restricted and are either exposed directly (such as Content-Type) or protected by the system and cannot be set in a WebHeaderCollection object. Any attempt to set one of these restricted headers in the WebHeaderCollection object using the Item[HttpRequestHeader] or Item[String] property or throws an exception. If the WebHeaderCollection object is associated with a HttpWebRequest object, the exception is thrown by the Item[HttpRequestHeader] property. If the WebHeaderCollection object is associated with a WebClient object, the exception is thrown when an attempt to send the WebClient request occurs.

For a list of restricted headers, see the Remarks in the WebHeaderCollection class.

Important Note:
In Silverlight for Windows Phone the list of headers that can be set is slightly different. For more information see Networking in Silverlight for Windows Phone.

Silverlight 2 and later have support for cross-domain connectivity which allows an application to access resources from locations other than the site of origin. This is an important feature for enabling Silverlight applications to consume existing services on the web. The security policy system in the Silverlight runtime requires that a policy file be downloaded from a network resource before a network connection is allowed access to that resource. This security policy system affects cross-domain network access for WebClient and HTTP classes in the System.Net namespace. Network connections for WebClient and HTTP classes to the site or host of origin do not require a security policy. For more information, see Network Security Access Restrictions in Silverlight.

For security reasons, the Silverlight runtime restricts access to certain classes of URLs from the WebClient and HTTP classes in the System.Net namespace. There are similar access restrictions applied by the Silverlight runtime to other classes including the Image and MediaElement classes in the System.Windows.Controls namespace. The Silverlight runtime also applies access restrictions to XAML source files and font files based on the class of URL.

The connections affected are access to cross-zone, cross-domain, and cross-scheme URLs. These restrictions are designed to prevent networking threats (for example, threats based on a Silverlight application run from an internet server getting access to resources on a local intranet server). For more information, see Network Security Access Restrictions in Silverlight and URL Access Restrictions in Silverlight.

For security reasons, the Silverlight runtime restricts the WebClient class from sending specific headers to a cross-domain site unless the header is allowed by the security policy applicable to the target cross-domain site. This restriction applies to resources from locations other than the site of origin. The Authorization header can be set using the Headers property. However to set the credentials properly, the cross-domain policy applicable to the target must have the http-request-headers set to allow the Authorization header to be sent.

Version Notes

Notes to Inheritors

Derived classes should call the base class implementation of WebClient to ensure the derived class works as expected.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

See Also

Reference

Other Resources